factors that influence subfertility

Conception is most likely to occur in the first month of trying (about a 30% conception rate). The chance then falls steadily to about 5% by the end of the first year. Cumulative conception rates are around 75% after six months, 90% after a year, and 95% at two years. Subfertility is defined as a failure to conceive after one year of unprotected regular sexual intercourse. It is usually investigated after a year, although for some couples it may be appropriate to start investigations sooner. The likelihood of spontaneous conception is affected by age, previous pregnancy, duration of subfertility, timing of intercourse during the natural cycle, extremes of body mass, and pathology present. A reasonably high spontaneous pregnancy rate still occurs even after the first year of trying.

Subfertility is a failure to conceive after one year of unprotected regular sexual intercourse. Subfertility can be primary or secondary Primary subfertility—a delay for a couple who have had no previous pregnancies.
Secondary subfertility—a delay for a couple who have conceived
previously, although the pregancy may not have been successful (for
example, miscarriage, ectopic pregnancy)

Age
A strong association exists between subfertility and increasing female age. The reduction in fertility is greatest in women in their late 30s and early 40s. For women aged 35-39 years the chance of conceiving spontaneously is about half that of women aged 19-26 years. The natural cumulative conception rate in the 35-39 age group is around 60% at one year and 85% at two years.

This marked, age related decline in spontaneous conception is also mirrored in the outcome of assisted conception treatment. Recent evidence shows that male fertility also declines with age. Genetic defects in sperm and oocytes that are likely to contribute to impaired gamete function and embryonic development increase with age. The age related decline in female fecundity is caused by a steadily reducing pool of competent oocytes in the ovaries.

It has been estimated that smokers are 3 times more likely to take more than a year to conceive than non-smokers, and in each cycle smokers have two thirds the chance of conceiving compared with non-smokers

Duration of subfertility
The longer a couple has to try to conceive, the smaller the chance of spontaneous conception. If the duration of subfertility is less than three years, a couple is 1.7 times more likely to conceive than couples who have been trying for longer. With unexplained subfertility of more than three years, the chances of conception occurring are about 1-3% each cycle.

Previous pregnancy
When a delay in conception has no obvious cause the likelihood of conception is increased 1.8-fold if the couple has secondary rather than primary subfertility. Timing of intercourse during ovulatory cycle The chance of conception in an ovulatory cycle is related to the day in the cycle on which intercourse takes place.

The window of opportunity lasts six days, ending on the day of ovulation. A study by Dunson et al (2002) showed that the probability of conception rose from six days before ovulation, peaked two days before ovulation, then fell markedly by the day of
ovulation. This shows that sperm need to be deposited in the female genital tract before ovulation to maximise chances of conception. This is consistent with the progesterone induced changes in cervical mucus that occur immediately after ovulation and impede the penetration of sperm.

Weight
Pregnancy is less likely if the woman’s body mass index (BMI) (weight (kg)/(height (m)2)) is > 30 or <> 30 need advice about modifying their diet and doing more exercise to lose weight and they should aim for a BMI < style="font-weight: bold;">

Other factors affecting fertility
The chance of conception may be reduced by smoking, caffeine, and use of recreational drugs. The effect of some of these factors may be attributed in part to an association with other factors that affect fertility, such as an increased risk of sexually transmitted infection.

Obesity is also associated with an increased risk of miscarriage and obstetric complications such as hypertension, gestational diabetes, thromboembolism, and complicated delivery.

The effect of alcohol on fertility is not clear as the results of studies are conflicting. Some studies have found impaired fertility in women drinking more than five units of alcohol a week, whereas others have found that low to moderate alcohol consumption may be associated with a higher conception rate than in non-drinkers. Excess alcohol consumption in men can contribute to impotence and difficulties with ejaculation and may impair spermatogenesis.